Catalysts based on metallocenes are known. In these organometallic complexes, a metal atom is sandwiched between two cyclopentadienyl ligands. The synthesis, structure and properties of these complexes is described, for example, by Nicholas J. Long in “Metallocenes” published by Blackwell Science, 1998.
Ligands containing heteroatoms of the electron-donating type, such as phosphorus, are also known. Thus, cyclopentadienyl-derived ligands in which a carbon atom is replaced with a phosphorus atom are known. These ligands are denoted by the term “phospholyl”.
Zirconium-based organometallic complexes comprising one or two substituted phospholyl ligands have been prepared. Their catalytic activity for the polymerization of ethylene is unsatisfactory (C. Janiak, U. Versteeg, K. C. H. Lange, R. Weimann and E. hahn, Journal of Organometallic Chemistry 501 (1995), 219-234).
Such substituted monophospholyls or biphospholyls of the (R1,R2,R3,R4,C4P)2ZrCl2 type are also known, for Example from E. J. M. de Boer et al., Journal of Molecular Catalysis A: Chemistry 128 (1998), 155-165. Their catalytic activity with regard to the polymerization of propylene has been evaluated. Only complexes with a phospholyl ligand carrying at least one aryl substituent in a position adjacent to the phosphorus show a useful activity.
It is also known to use as catalyst complexes whose ligands are mutually bridged. In particular, application WO 98/41529 discloses bridged monophospholyl complexes of the [α-SiMe2(3,4,5-trimethylphosphole, NtBu] TiCl2 type. In such complexes, the metal is linked to a phosphorus atom and to a nitrogen atom.
Application WO 98/01485 discloses monophospholyls of the type bridged by a donor-acceptor type link between the phosphorus and the boron P→B:[2,3,4,5-pentamethylphosphole,Me2B-Cp]TiCl2.